This invention relates to an air extraction apparatus of the kind defined in the preamble of claim 1.
These days, there often exists, in food service, and especially in food service systems and communal catering in cafeterias and the like, i.e. in situations in which the guests serve themselves, the requirement that cooking, grilling or baking be done right before the guest""s eyes. In this so-called up-front cooking there exists the problem that the fumes which are created thereby have to be removed. Because stationary fume extraction hoods are often not available or suitable and transportable fume extraction hoods are often not available or applicable, there has already been developed a mobile cooking station (cf. the SMOKE-STOPP catalog of the Bohner Company for the year 2000) and a stationary kitchen module (cf. the article xe2x80x9cOdorless Before The Eyes Of The Guestsxe2x80x9d in the magazine Cooking Practice and Community Food Supply, October 1999, page 52), which are provided with an air extraction apparatus of the kind defined in the preamble of claim 1. In the known air extraction apparatus which sometimes involve a grill, the two air openings on both sides of the work station serve for rim extraction. Because extraction is performed at both lateral rims of the work station, the extraction effect above the middle of the work station is naturally relatively slight. Therefore, a large area above the work surface is not efficiently encompassed by the air current drawn in at the rims. A particular disadvantage of rim extraction is that uncleansed room air is drawn partly across the work station. In addition, for integrated odor elimination, the known air extraction apparatus has, in a substructure below the work station, several pre-filters, several fabric filters and several activated carbon filters, between which there is located an exhausting device which provides bidirectional suction. The whole lower surface of the substructure is occupied by a grease-collecting pan. This filter arrangement requires work and is expensive, because the activated carbon filters have to be changed frequently and constitute an environmental burden.
Indeed, an odor extraction apparatus known from DE 2 402 615 A1 can make do with a simpler filter arrangement for grease separation and odor removal, but a suction funnel with a grease retention filter is positioned above the work station, and that requires an upwardly directed air flow in order to produce an air curtain for screening the work station.
From U.S. Pat. No. 3,260,189 there is known a ventilating system in which there is provided, above the work station, an extraction apparatus inclined diagonally with respect to the work station and provided with several grease filters. Air which exits on one side of the work station from a blower slot is thus guided over the work station diagonally upwardly to the extraction device. Furthermore, in this known ventilating system, no special precautions for odor elimination are taken.
The object of the invention is to so improve the extraction in an air extraction apparatus of the kind initially described that the extraction process effectively encompasses the whole work area and that food on the work station does not come into contact with uncleansed ambient air.
This object is achieved according to the invention by an air extraction apparatus having the characteristics stated in claim 1.
In the air extraction apparatus according to the invention, there is formed an air circulation loop which extends across the whole work station, above which it creates an air curtain. The air curtain is formed by air which flows out of an air opening on one side of the work station and flows into an air opening on the opposite side of the work station. Thus, the air curtain produced by the air extraction apparatus according to the invention covers the whole area above the work station. The air which forms the air curtain is ambient air, i.e. air which flows over the work station only after it has been drawn through the filter arrangement by means of the suction blower, and is therefore cleansed air. The compact housing of the blower and the filter arrangement in a separate space, located in the air circulation loop and connected to the air openings on both sides of the work station, makes it possible for the air extraction apparatus according to the invention to separate, within limited space inside the air loop, grease from the air and simultaneously free it from odors. In the air extraction apparatus according to the invention, the air to be cleansed is drawn in through the grease separating filter and pushed out through the odor filter. Since a grease separating filter and an odor filter have different pressure drops, the inventive arrangement of the two filters, respectively upstream and downstream of the blower, makes it possible to adjust the air velocity optimally for the respective filters.
Since, in the air extraction apparatus according to the invention, the air circulation loop provides an air outlet for a portion of the air from this air circulation loop, a portion of the air in the air circulation loop can be continuously replaced by ambient air which is then also led first through the filter arrangement before it contributes to the formation of the air curtain above the work station.
Because, in an air extraction apparatus according to the invention, the opening of the air outlet can also be adjusted in size, the fraction of fresh ambient air in the air circulation loop can be adjusted as needed. Further, because in the air extraction apparatus according to the invention, the air outlet is located downstream from the blower, the air has passed through the filter arrangement and is therefore already cleansed before it escapes into the ambient. Further, because in the air extraction apparatus according to the invention, the blower is located between at least two filters of the filter arrangement, the blower is protected from becoming dirty. Further, because the filter upstream from the blower is a grease separating filter and the filter downstream from the blower is an odor filter, the blower is especially little adversely affected by air loaded with grease and the ambient air which is led back to the work station is not only grease- but also odor-free.
Indeed, from DE 473883C it is in fact already known to provide, in a system for protecting work spaces from the vapors coming from open vessels and other air uncleanliness, by means of an air curtain, a blower which simultaneously serves to create the air flow and to remove the vapors, whose intake duct segment opens into a funnel located above the edge of a container, whereas its pressure duct segment has a nozzle at the opposite container edge directed toward the funnel from which an outlet duct branches off, but in this known apparatus there are no means at all for grease separation or odor elimination. The air outlet leads simply into open space.
Preferred embodiments of the air extraction apparatus according to the invention are the subject of the dependent claims.
If, in an embodiment of the air extraction apparatus according to the invention, the blower is a centrifugal blower, both structural and flow-technology advantages are achieved in the construction of the air extraction apparatus.
If, in a further embodiment of the air extraction apparatus according to the invention, the grease separating filter is a cyclone filter, as manufactured, for example by the Renchler and Reven Company, 99.5% of the grease entrained in the exhausted air can be separated. Further, such a filter is very maintenance friendly, because it can be simply washed out in a dishwasher and then reinstalled.
If, in a further embodiment of the air extraction apparatus according to the invention, a grease collecting pan is installed below the grease separating filter, the grease separated by the grease separating filter can be collected in simple manner.
If, in a further embodiment of the air extraction apparatus, the odor filter is a zeolite filter, then this odor filter can be easily re-generated and is therefore especially maintenance and environment friendly.
If, in a further embodiment of the air extraction apparatus according to the invention, the air circulation loop has two vertical air channels in the region below the work station, above which the space that houses the blower and the filter arrangement is connected with the air openings on both sides of the work station, then the equipment required for supplying heat to food such as a cook top or a grill plate can be conveniently housed in the space between the vertical air channels, together with the electric current supply and its accompanying controls.
If, in a further embodiment of the air extraction apparatus of the invention, the space in which the blower and the filter apparatus are housed is located beside the work station, then the path which the air loaded with grease and odors has to follow is minimized, starting from the downstream air opening of the work station to the filter apparatus, so that the possibility that the air extraction apparatus can be dirtied by grease is also minimized.
If, in a further embodiment of the air extraction apparatus of the invention, the grease separating filter and the odor filter are inclined from the vertical, then technological benefits of construction and flow arise, because the space between the two filters which houses the blower can be well used, or because the filtering effect is especially good in such a configuration.
If, in a further embodiment of the air extraction apparatus of the invention, the grease separating filter is inclined from the vertical by an angle of 40-50xc2x0, preferably 45xc2x0, and if, in a still further embodiment of the air extraction apparatus of the invention, the odor filter is inclined from the vertical by an angle of 30-40xc2x0, preferably 35xc2x0, especially great technological benefits accrue in construction and in air flow, as has been demonstrated by means of a prototype.
If, in a further embodiment of the air extraction apparatus of the invention, the space in which the blower and the filter apparatus are housed, is divided by the two filters into a pre- and post- (blower) chamber, then the space available below the work station or alongside the work station is especially well used.
If, in a further embodiment of the air extraction apparatus of the invention, the air outlet is located in a wall of the post- (blower) chamber, odor and grease-free air can be ejected into the ambient, because this air has already flowed through the entire filter apparatus.
If, in a further embodiment of the air extraction apparatus of the invention, the work station is a grill, which is located above the space in which the blower and filter apparatus are housed, or which extends alongside that space, the technological flow advantages achieved by the invention manifest themselves because the air curtain covers the whole region above the grill, so that, also during grilling, neither odors nor grease reach the surrounding space.
If, in a further embodiment of the air extraction apparatus of the invention, the air outlet is so formed or adjusted that 75% of the air is extracted from the air circulation loop and the remaining 25% reach the work station as ambient air and form its air curtain, then the space surrounding the work station is especially effectively protected from odors and grease, since tests have shown that such an air curtain, which contains only 25% of the air originally drawn into the air circulation loop, can be completely drawn into the air opening on the downstream side of the work station, without causing an air blockage to form in front of this air opening.
If, in a further embodiment of the air extraction apparatus of the invention, there is provided at least one air intake for drawing in ambient air into the air circulation loop for replacing the air which escapes from the air circulation loop into the surroundings via the air outlet, the supplementation by room air to replace the air escaped via the air outlet can be controlled as required by the location of this air intake. Through this air intake, the air volume flowing into the grease filter is increased. This reduces the fume density and simultaneously lowers the air temperature, both of which are important for the optimum efficiency of the odor filter. The reduction in fume density prevents quick saturation of the odor filter. Thus, the air intake effects a reduction in fume density, and an associated temperature reduction of the unfiltered air, which is again important for the operation of the odor filter, especially when this involves a zeolite filter.
If, in a further embodiment of the air extraction apparatus of the invention, the air intake is the air opening on the downstream side of the work station, then it follows that the cleansed air curtain covers the entire work station, so that no uncleansed ambient air reaches the food on the work station, and yet the extracted air can be replaced by fresh ambient air.
If, in a further embodiment of the air extraction apparatus of the invention, the air intake is an additional air opening positioned downstream from the air opening on the downstream side of the work station and upstream from the blower, then the exhausted air in the air circulation loop can be controllably replaced as needed, without detriment to the air curtain and its functioning above the work station. The secondary air drawn in by the additional air opening has the effect of significantly increasing the air volume to be treated by the filters, which is loaded with fumes and odors. That is because the volume of air flowing to the grease filter is increased by the air opening. The fume density is thereby reduced. At the same time, the air temperature is lowered. Both components are quantities which determine the optimum effectiveness of the zeolite filter. The reduction in fume density prevents rapid saturation of the zeolite filter. Thus, for heavy fume/odor incidence, the filter operation of the zeolite filter is optimized. Simultaneously, the resulting air quantity increase leads to a temperature reduction of the air extracted from the work station, which is also advantageous for the optimal operation of the zeolite filter. These advantages prevail overall in the previously mentioned further embodiment of the air extraction apparatus of the invention, in which there is provided at least one air intake for drawing ambient air into the air circulation loop to replace the air which escapes via the air outlet from the air circulation loop into the surroundings.
If, in a further embodiment of the air extraction apparatus of the invention, it is integrated into a kitchen work station to form a kitchen module, that module can be inserted into a modular kitchen equipment suite such as the varithek(copyright)-System, known from German patent DE 197 57 004 A1.
If, in a further embodiment of the air extraction apparatus of the invention, the two air openings are so located relative to each other that an air flow axis which symbolizes the air curtain is inclined slightly downward from the horizontal with respect to the downstream air opening, then the slightly downward directed air flow better counteracts a heat flow which forms above the work surface than would, for example, a horizontal air flow. With the latter, there is the risk that the heat flow carries grill and cooking vapors beyond the effectiveness range of the downstream air opening, so that these vapors cannot be, or can only be partially encompassed.
If, in a further embodiment of the air extraction apparatus of the invention, the upstream air opening takes the form of a narrow outlet slot and the oppositely located downstream air opening takes the form of a substantially wider suction slot, then the encompassing effect, i.e. the effect that the downstream air opening encompasses the supplied air as completely as possible, can be optimized. In so doing, the outlet slot is preferably made narrower for a wide spacing between upstream and downstream air openings, than for a small spacing between the two air openings. The width of the suction slot is preferably made larger for a wide spacing between the air openings than for a small spacing.
If, in a further embodiment of the air extraction apparatus of the invention, the outlet slot and the suction slot are formed by air duct elements in the vertical air channels, then the air duct elements in the vertical air channel of the upstream air opening make it possible to concentrate and deflect the upwardly flowing air, the upward narrowing of the channel and the deflection being so configured that turbulence is prevented as much as possible and that the least possible pressure loss takes place. In the downstream air opening forming the suction slot and a vertical air channel connected thereto, the air is deflected by sheet metal guidance elements and the encompassing effect of the suction slot is substantially improved by this flow optimizing configuration.
If, in a further embodiment of the air extraction apparatus of the invention, the outlet slot is inclined slightly downward from the horizontal, and the suction slot is provided with radii on its facing internal walls, then the encompassing effect of the downstream air opening forming the intake slot can be optimized, preferably by radii at the upper and lower edge of the intake slot.
If, in a further embodiment of the air extraction apparatus of the invention, a section of the vertical air channel which extends from the downstream air opening is covered upwardly by an air guiding element, then the encompassing effect of the downstream air opening can be optimized from the current flow technology standpoint. Preferably, the air guiding element is formed with a small working surface, or at a short distance between the upstream and downstream air opening, as a radius on the upper edge of the downstream air opening. For a large working surface, or a wide spacing between the air openings, the air guiding element is preferably S-shaped at the transition from the downstream air opening to the vertical channel.
If, in a further embodiment of the air extraction apparatus of the invention, the covering upper air guiding element is increasingly foreshortened with increasing size of the working space, and therefore increasing distance between the upstream and downstream air openings, then part of the encompassing effect of the downstream air opening is thereby deflected upwardly and optimized. This is due to the creation of an increasing quantity of vapors due to an increasing distance between the upstream and the downstream air opening, as well as the upward heat flow of the upwardly deflected air stream of the upstream air opening.
If, in a further embodiment of the air extraction apparatus of the invention, the air guiding element has an S-shaped cross-section, then this has the advantage that, for a greater distance between the upstream and downstream air openings, the transition from the downstream air opening to the vertical channel is optimized from the flow technology standpoint. Especially improved is the encompassing effect of the downstream air opening.
If, in a further embodiment of the air extraction apparatus of the invention, the work station above the air openings is surrounded on three sides, not including its operator side, by an air guiding wall, especially a splash guard, which increases in height from the operator side in the direction transverse to the air curtain and toward the opposite side of the work station, there is produced an air flow (outlet stream) which moves in a stable whirling pattern from the air opening on one side to the air opening on the other side of the work station. This is associated with a lengthening of the air path. This again increases the take-up capacity for the fumes to be transported away. In this regard, the air guiding wall plays an important role. In a further embodiment of the invention this consists of a U-shaped rim-encircling metal sheet which serves as a splash guard for grilling but, in this embodiment of the invention, has the additional effect that the above-mentioned whirling flow is reliably stable. Only the geometric configuration of the air guiding wall or the splash guard according to the above-described embodiment of the invention, leads to the optimum whirling flow. In so doing, the increasing height of the guiding wall in the rear of the work station away from the operator side plays a special role. This means that its shape decisively affects the aerodynamics.